In a typical wireless communication network, radio capable devices, also known as wireless devices, mobile stations and/or user equipments (UEs), communicate via a wireless medium e.g. a radio channel e.g. via a Radio Access Network (RAN) or directly. Wireless Local Access Network (WLAN) systems based on IEEE 802.11, used for example in Industrial, Scientific and Medical (ISM) bands, access a wireless medium via contention based protocols complying with different regulatory domains. These types of systems are commonly referred to as Carrier Sense Multiple Access (CSMA) systems. WLAN systems are designed to support a plurality of services e.g. an IEEE 802.11ah system is designed to support large number of radio capable devices with low traffic profiles. By definition, a contention based protocol allows multiple radio capable devices to share the same spectrum by defining events that occur when two or more radio capable devices attempt to simultaneously access the same wireless medium and establishing rules by which a radio capable device provides reasonable opportunities for other radio capable devices to operate on the same wireless medium. In the standard IEEE 802.11 radio capable devices are referred to as Stations (STA) and Access Points (AP).
Receivers of STAs may not always be powered on, which means STAs may be in a doze-state. In addition, 802.11 STAs use Distributed Coordination Function (DCF) or Enhanced Distributed Channel Access (EDCA) as contention based access functions. The DCF is a basic contention based function where STAs access the shared wireless medium with similar access parameters. Thus, the access procedure of the DCF does not offer differentiated Quality of Service (QoS). EDCA is a contention based function where STAs access the shared wireless medium with differentiated access parameters. Currently the standard 802.11ah supports two types of devices: Sensor type STAs, including Energy Limited STAs, and non-sensor type STAs. Implicitly these are battery powered or electrical grid powered. The EDCA access parameters are dependent on the access category of packets/flows and in 802.11ah also on the type of the STA. Thus, the EDCA provides differentiated Quality of Service (QoS) at a Medium Access Control (MAC) level.
The access procedure for the DCF is as follows: A STA determines whether a wireless medium is idle via a Channel Sensing (CS) function in two different time intervals. The first time interval is a deterministic time DCF Interframe Space (DIFS) and its duration is specified according to a physical layer technology in IEEE 802.11/IEEE 802.11ah. The second time interval is a back-off time is a random time that STAs are required to sense the wireless medium before starting transmission. After the STA has determined that the wireless medium is idle, the transmission can begin. Otherwise, the STA has to wait until the wireless medium is idle and follow specific procedures defined in IEEE 802.11/IEEE 802.11ah.
The access procedure for the EDCA is as follows: A STA determines whether the wireless medium is idle via the CS function in two different time intervals. The first time interval is a deterministic time Arbitration Inter-frame Space (AIFS) with a duration that is defined as AIFS=SIFS+AIFSN*aTimeSlot, where SIFS means Short Interframe Space and AIFSN means Arbitration Interframe Space Number and is dependent of traffic/flow access category in IEEE 802.11 and also type of STA in IEEE 802.11. The second time interval is a back-off time is a random time that STAs are required to sense the wireless medium before starting transmission. After the STA has determined that the wireless medium is idle during both the AIFS and the back-off time, the transmission can begin. Otherwise, the STA has to wait until the wireless medium is idle and follow specific procedures defined in IEEE 802.11/IEEE 802.11ah.
In the IEEE 802.11 there is also a Point Coordination Function (PCF) defined for channel access. PCF is meant to work with DCF and provide a contention-free access controlled by a capable Access Point (AP) called ‘PC’. A contention-free period starts when the access point gains control of the wireless medium by determining the wireless medium is idle during a PCF Inter-frame Space (PIFS) period defined as PIFS=SIFS+aTimeSlot. A PIFS is smaller than a DIFS.
The access parameters of the EDCA procedure are based on access category of packets/flows in IEEE 802.11 and also on type of STA in 802.11ah. The EDCA procedure gives access priority to sensor devices over non-sensor devices. Also, the DCF procedure does not provide differentiated access to any device type in WLAN. This results in wireless communication networks that handle access to wireless media randomly or based on whether the radio capable device is of a sensor type or not, this in its turn leads to a nonflexible solution with a reduced performance of the wireless communication network.